This invention relates to the method of making catheters and more particularly to the method of making a catheter having integral Luer locking means thereon.
Intravenous catheter placement units, for example, generally include a syringe with a hypodermic needle and a plastic catheter or cannula disposed on the needle. The plastic cannula for such a unit usually has a conical or Luer tapered connector at the proximal end, and a main catheter portion of relatively smaller diameter connected to the connector. The connector portion and main catheter portion may be economically and inseparably connected by integrally forming them to form a single-piece cannula. As is well known, the distal ends of the needle and cannula in such a unit are inserted into a body vessel, such as a vein, and proper placement of the cannula verified by effecting aspiration of blood into the syringe. The syringe and needle are then removed from the cannula, and, where infusion of fluid is to take place, a tube or infusion catheter having a male Luer connector is connected to the connector portion of the cannula to effect a Luer slip fit. While a Luer slip connection between the intravenous cannula and tubing is generally reliable, it is often desirable or necessary to have a Luer locking connection to positively insure against separation and leakage of fluid under many conditions of use, for example, where the catheter is to be used in critical situations or over a relatively long period of time, such as during infusion of a liquid. Some cannulas have been provided with Luer locking flange means at the proximal connector end thereof for this reason, however, there have been certain undesirable aspects associated with the manufacture of such cannulas. Two-piece catheters have been made in which the main portion of small diameter is extruded and a separate injection-molded Luer lock connector attached, such as by an adhesive. However, this method was relatively expensive and there was the possibility of the pieces separating under fluid pressure conditions. Also, single-piece catheters having an integral Luer lock connector have been made by the injection molding process but it has been difficult to obtain cannula walls which are thin enough in the distal or insertion portions of the catheter and which provide the desired flexibility, especially in the smaller sizes, such as 16, 18 and 20 gauge catheters. This tends to cause trauma and tends to undesirably affect the flexibility, handling, and flow characteristics of the catheter. Also, the injection molding process does not lend itself to the production of catheters or tubing of relatively long lengths because of the requirement of a correspondingly relatively long and costly mold.